The current 3GPP protocol provides that after entering the call status, the bearing control function, after receiving the 200OK confirmation message of the UPDATE message, starts the threshold control of the grouping classifier, that is, makes the media modification and switching operation become effective.
Referring to FIG. 1, the calling party and the called party modifies the media through the Re-INVITE transaction, and the bearing control function, when receiving the confirmation message (200 OK) of the UPDATE message, makes the media modification and switching effective, and the following problems exist:
1, considering the precondition, at this time the resource reservation of a certain direction is possibly not completed yet, and when the resource is not available, it is set to be effective prematurely;
2, the called user may require the manual confirmation for the media modification and switching operation, and before the user confirmation, it is set to be effective prematurely, and in the case that the user rejects it, many subsequent redundant steps will be produced.
3, the media channel is opened before the 200OK of the Re-INVITE message is confirmed, and the user may embezzle the bearing resource.
Therefore, the 200OK confirmation message of the UPDATE message during the Re-INVITE transaction process is unable to act as the confirmation of the media modification and switching.
At the same time, the case of the multimedia stream is considered, such as the audio stream modification coding and decoding format, and at the same time the video stream is added. The video stream may require the user confirmation, therefore, its bearing control function can regard the 200OK of the Re-INVITE as the final confirmation; however, the user, after completing the first media offer/answer process in the Re-INVITE, can possibly start using the new audio coding and decoding, therefore setting the effectiveness of the new parameter of the audio stream should not be delayed after receiving the 200OK confirmation message of the Re-INVITE.